In W5-1 "Shy Guy Jungle" there is an area of the level that features a trash heap. Mario can pick up some scraps of trash that normally have miscellaneous memo-esque fluff written on them, except for one particular scrap. This scrap has a code written on it, in the following format:
I've done a bit of looking around online, and have found that others have found the exact same code, or a similar code (only one character is different here, so I believe that this may actually be a typo) but nobody has, to date, found a use for the code.
It may simply be another piece of trash, because Mario reacts with a frown in a similar manner to the way he does with the remaining pieces of trash. Does anyone have any additional insight to this?